A number of rotary blood pumps presently are under development for application as either artificial hearts or cardiac assist devices. An axial flow blood pump, for example, typically includes a pump housing that defines a blood flow channel, an impeller mechanism mounted within the blood flow channel, an electric motor rotor coupled to actuate the impeller mechanism for blood pumping action, and an electric motor stator for actuating the rotor by electromagnetic force. The impeller mechanism may take the form of blades that are mechanically coupled to the rotor via a transmission shaft. Alternatively, the impeller blades can be mounted directly on the rotor. In this case, the rotor may form an elongated member that extends axially along the blood flow path. The impeller blades may be mounted about the rotor, for example, in a spiral-like pattern. The rotor is mounted in a bearing assembly.
Performance, reliability and longevity are critical performance factors for blood pumps due to their use as artificial hearts and/or cardiac assist devices. Among the most critical components of the pump is the motor. When the motor fails, the pump fails, leaving the residual function of the heart as the only means for continued cardiac operation and survival. Motor performance is highly dependent on the operation of the motor rotor and bearing assembly. The bearing assembly can be susceptible to seizure due to thrombosis at the bearing interface that restricts rotor movement. Excessive heat and/or inadequate heat removal near the bearing assembly can also lead to bearing seizure. To minimize the incidence of seizure and reduce wear, the bearing assembly ordinarily must be constructed to aggressive tolerances that drive up the cost and complexity of manufacture. In artificial heart applications, notwithstanding cost and complexity of manufacture, bearing failure can be catastrophic. Accordingly, bearing design improvements remain a constant focus for the blood pump industry.